A classical error channel is built from exact prepared-label counts. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Counts define a classical error channel
Prepared zero gives 18 stays and 2 flips. Prepared one gives 3 flips and 17 stays.
zero row (18,2),one row (3,17)
Prepared-label rows expose both error rates
The channel has a zero-prepared row, a one-prepared row, and a conserved row sum.